The RC-135U is tasked with strategic reconnaissance and technical intelligence (TECHINT) gathering on radar/emitter systems.
Three Combat Sent aircraft were converted from RC-135Cs in 1970-71 to fill a
critical need for data collection on adversary radar threats and defenses. 
Combat Sent’s distinctive chin and wingtip antenna arrays, large cheekfairings, and extended tail contain specialized sensor suites to collect data and analyze airborne, land, and naval radar/emitter systems.
Each airframe incorporates a different, tailored sensor suite, and the data gathered is critical to the effective design and programming of RWR (radar warning receivers), jammers, decoys, anti-radiation missiles, and threat simulators. Combat Sent additionally enables strategic analysis for National Command Authorities and combatant forces.
The aircraft utilizes radar/solid-state doppler, INS, celestial, and GPS for navigation, and is capable of both operator, automated, and blended signal gathering and analysis.
Continuous baseline upgrades keep the fleet viable through 2040, and flexible funding permits rapid variant-specific mods in response to emerging/evolving threats. FY21 focus on completing Baseline 5/6 upgrades (similar to Rivet Joint Baseline 12) including wideband SATCOM reachback, integrating Rivet Joint’s COMINT suite, improving operator interface, enhancing antennas and processors, and capability upgrades for dense signal environments.
Contractors: Boeing (airframe); L3Harris; Textron.
First Flight: N/A.
Delivered: May-December 1971 (RC-135U).
IOC: 1971.
Production: Three converted.
Inventory: Two.
Operator: ACC.
Aircraft Location: Offutt AFB, Neb.; forward operating locations: Al Udeid AB, Qatar; NSF Diego Garcia, U.K.; Eielson AFB, Alaska; Kadena AB, Japan; RAF Mildenhall, U.K.; NSA Souda Bay, Greece.
Active Variant: •RC-135U Combat Sent. Modified C-135 equipped for radar/emitter analysis.
Dimensions: Span 135 ft, length 140 ft, height 42 ft.
Weight: Max T-O 322,500 lb.
Power Plant: Four CFM International F108-CF-201 turbofans, each 21,600 lb thrust.
Performance: Cruise speed 517 mph, range 4,140 miles, 8-hr normal endurance, 24-hr crew endurance (farther with air refueling).
Ceiling: 42,000 ft.
Accommodation: Two pilots, two navigators, three airborne systems engineers; Mission crew: 10 EW officers, six or more electronic, technical, mission-area specialists.